SQLite NULL Values

SQLite'sNULLis a term used to represent a missing value. A NULL value in a table is a value shown as blank in a field.

A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different from a zero value or a field containing spaces.

Syntax

Used when creating a tableNULLThe basic syntax is as follows:

SQLite> CREATE TABLE COMPANY(
   ID INT PRIMARY KEY     NOT NULL,
   NAME           TEXT    NOT NULL,
   AGE            INT     NOT NULL,
   ADDRESS        CHAR(50),
   SALARY         REAL
);

Here,NOT NULLIndicates that the column always accepts explicit values of the given data type. There are two columns where we did not use NOT NULL, meaning these two columns can be NULL.

A field with a NULL value can be left empty when the record is created.

Example

NULL values can cause problems when selecting data, because when an unknown value is compared with another value, the result is always unknown and will not be included in the final results. Suppose there is the following table, the records of COMPANY are as shown below:

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22          South-Hall  45000.0
7           James       24          Houston     10000.0

Let us use the UPDATE statement to set some values that allow null to NULL, as shown below:

sqlite> UPDATE COMPANY SET ADDRESS = NULL, SALARY = NULL where ID IN(6,7);

Now, the records of the COMPANY table are as shown below:

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22
7           James       24

Next, let's look atIS NOT NULLthe usage of the operator, which is used to list all records where SALARY is not NULL:

sqlite> SELECT  ID, NAME, AGE, ADDRESS, SALARY
        FROM COMPANY
        WHERE SALARY IS NOT NULL;

The above SQLite statement will produce the following result:

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0

Below isIS NULLthe usage of the operator, which will list all records where SALARY is NULL:

sqlite> SELECT  ID, NAME, AGE, ADDRESS, SALARY
        FROM COMPANY
        WHERE SALARY IS NULL;

The above SQLite statement will produce the following result:

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
6           Kim         22
7           James       24